French patent specification U.S. Pat. No. 4,800,049, in the name of ANVER describes a method and apparatus for manufacturing molded objects out of plastic material from a liquid plastisol which is injected into a mold, which mold is subjected to the action of a high frequency electric field from a suitable generator. Such a technique is used, for example, for manufacturing articles of leather goods or parts for shoes. In order to extend the method and the apparatus implementing the method to other applications, such as manufacturing overmolded parts e.g. car windows with integrated peripheral seals, ANVER has already proposed (in U.S. Pat. No. 4,954,073, filed May 4, 1988) an improved method and apparatus suitable for use with plastisols or other liquid plastic materials, in particular those of the polyethyl or polyurethane type.
The method and apparatus described in the above-mentioned U.S. Pat. No. 4,954,073 give full satisfaction. However, manufacturing throughput is not as high as could be desired and this is because implementation of the method requires that the two half-shells of the mold should be kept pressed against each other for a certain length of time after the high frequency field has been applied. In an apparatus having a single field generator, this is done by keeping the mold locked shut for several minutes between the plates of a press associated with the generator. The generator is therefore not available during this period of time which is the time during which polymerization takes place, and high throughput can thus be obtained with the apparatus only by an installation of the carousel type or by means enabling the generator to be displaced, both of which solutions are mechanically complex and expensive. The same applies to the installation described in U.S. Pat. No. 3,444,275 where a press is mechanically locked under the control of an actuator.
Consequently, a general object of the invention is to provide a method and an installation for high frequency molding of plastic material enabling high manufacturing throughput rates to be obtained in an installation having a generator associated with a press.